Carburizer



Patented Dec. 18,1928

UNITED STATES PATENT OFFICE.

FREDERICK O. LANGENBERG, OF WATERTOWN', MASSACHUSETTS, ASSIGNO R TO E. I. HOUGHTON AND COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

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No Drawing.

My invention relates to that class of com-' pounds known as carburizing or case hardening materials. One object of my invention is is to provide a new and novel compound which is a departurefrom the usual type of compounds used in carburizing and case hardening work.

Another object of my invention is to provide a means of greatly increasing the efi'iciency of the present carburizers as well as increasing their length of life.

Another object of my invention is to provide a new carburizer or case hardener which will secure the same depth of carbon penetration in a much more reduced time than has heretofore been known as'well as permit the carburization to take place at an appreciably lower temperature.

A further object of my invention is to pro vide improved carburizing or case hardening materials or compounds having as one constituent a new type of material which is not in itself an energizer of the customary type but which in the presence of the carburizing materials functions as a substance which greatly increases the efiiciency of the carburizer.

Still another object is to provide a new and improved method of carburizing and case hardening. Other objects will be apparent upon consideration of the specification and claims.

My, invention is characterized by the employment ofcertain accelerating substances in conjunction with any given type of carburizer or case hardening material. The term accelerating'substance'is used to designate those compounds which in themselves do not possess any carburizing action or which possess such slight activating properties that they are not classed as activators when used in the amounts contemplated here, but which due to their inherent properties remarkably increase the activity, efiiciency, intensity and duration of life of the compounds.

Another function of the addition of the accelerating substance is to materially cut down the length of time of treatment. I have found, for example, that by the addition of an accelerating substance to a known carburizer I that the same depth of penetration of the carbon by the steel will take place in about one half the time. Furthermore, the temperature of .carburization necessary to form a satisfactory case may be materially lowered when tion to Application filed March 22, 1927. Serial No. 177,4 70.

mg substance. The usual temperature of carburization is between 850 C. to 950 (3., that is from 100 to 150 above the critical a carburizer is used containing an accelerattemperature is approximately the critical temperature of the majority of steels and since grain growth does not occur until the critical point of the steel is passed, it is possible by the use of my compound to prevent excessive the accompanying weakening of the structure of the steel.

The phenomenon of case hardening is not definitely understood and the theories at the present time are not conclusively proved. One theory which has been accepted is based on the assumption that the case hardening action depends on the conversion of carbon monoxide to carbon dioxide and the giving up of carbon to the steel. The equilibrium ratio of the carbon dioxide to carbon .monoxide grain growthand thereby'pre'vent at the temperature of carburization is therefore an important governing factor. If this equilibrium can be so disturbed that more carbon monoxide will be converted to carbon dioxide, a more 'efi'ective carburizer will result. My invention contemplates the addithe carburizer of a substance which probably exerts. an influence upon the equilibrium of the carbon dioxide and carbon monoxide, increasing the conversion of can bon monoxide into carbon dioxide.

This theoretical discussion is merely to be considered as such and not in any way binding upon the invention whichbroadly comprises the addition of an accelerating substance to the carburizing and case hardening compounds to enhance greatly their activity and effectiveness. accelerating substances may be of a wide variety of compounds but ingeneral belong to the classification known in chemistry as the oxides or oxide engendering compounds. The latter term includes those salts which are sufiiciently unstable at the carburizing temperatureto decompose into one or more nongaseous oxides.

I have found that these I am aware that some alkali and alkaline A earth oxides have heretofore been used but this is not part of my invention since these oxides function as energizing materials per se of nickel, cobalt, iron, zirconium, manganese,

and do not function in the accelerating sense chromium, silicon, aluminum, and uranium have proved to have marked accelerating qualities, butthis list is not inclusive and I Wish it to beunderstood that my invention contemplates the use of any oxide which acts as an accelerating substance on the chemical reactions that occur in the case-hardening or carburizing operation. Of the second class, that is those compounds which decompose to give oxides, the organic compounds of the-metals .and the decomposable inorganic compounds of the metals might be mentioned. Iron oxalate, cobalt acetate, iron chloride and the like are examples of this second class.

- I have found that the compounds of the metals iron, nickel and cobalt, particularly of the two last named, are especially of value as activators. These three metals are grouped under Group VIII of the Periodic Table of Mendeleeff and Meyer to be found on page'808 of Modern Inorganic Chemistry by J. W. Mellon, published by Longs ,mains, Green. and Company of London, 1920.

Furthermore, the compounds which are within the contemplation of my invention may be reduced either wholly or partially to the metal by the carbon and carbon monoxide .1 existing in the carburizing pot, and it may be that the accelerating action is due at least in part to this reduced metal. However, this is merely a theoretical digression as far as this application is concerned for, throughout the specification and claims where the term non-gaseous oxide at the temperature of carburizationi is used, I intend that it shall cover that portion, if any, of the oxide which has been reduced in the carburizing pot to the metal.

The accelerating substance may be incorporated'into any one of the known carburizers in any variety of ways either during the manufacture of the carburizerdtself or subsequent thereto. The accelerating substance may be mechanically tumbled in a powdered condition with the well-known energizers, such as barium and calciumcarbonate, and

the grains to be activated until the charcoal or a .91, and vanadium .15.

coke grains or both have become permeated accuses with the powdered material or the powdered material has become frictionally adherent thereto. If desired after the tumbling, a binder such as black strap molasses or hydrocarbon oil may be added to prevent the ener- .gizer and accelerating substance from dusting ofli in transit and in use and the grains may then be treated with a powdered material such as charcoal dust to prevent them from caking. The grains to be activated may be treated with the binder prior to the treatment with the energizer and the accelerating substance or dust, or simultaneously with the binder.

If a carburizer is to be used in a powdered form instead of in granular form, the accelerating substance may be intimately mixed by simply grinding it with the other ingredients including the carbonaceous material and the energizers and the piece to be carburized placed in this powder, or as is well known the mass may be mixed with a moistening material, such as oil or molasses and the carburizing. compound applied in the form of a surface paint or paste- .lVith the accelerating substances that are soluble, for example some of the organic salts of metals, the accelerating substance may be dissolved in water and this solution either applied to the carbonaceous granules or mixed with the powdered material if that type of carburizer is to be made. vides a means for thoroughly impregnating the grains or for intimately dispersing the accelerating substance in the compound, thus insuring a more intimate contact than is otherwise possible. Further methods of forming the carburizer will be evident to one skilled in the art and need no detailed description here. In general, it should be borne in mind that the more intimately that the accelerating substance can be brought into contact with the carbonaceous anaterial and the energizer, the more effective will be its action.

The percentage of the accelerating substancerrequired will depend upon the nature of the accelerating substance itself as well as on the nature of the material to which it is applied and the work for whichthe carburizer is intended. In certain cases, as small an amount as one-quarter of one per cent has proved to intensify remarkably the action of the carburizing compound. The upper limits vary widely and I do not wish to be limited to any particular percenta e although practically it is seldom that a larger amount than five percent is used.

A carburizer having for itsbase finely divided. spent bone was used to case-harden a steel having the following analysis :carbon .22, manganese .52, silicon .235. sulphur .021, phosphorous .010, nickel .09, chromium The piece was kept at a carburizing temperature of 9259 C. for

This solution method profive and three-fourth hours and after cooling the total case was measured. To a sample of this same carburizer, certain percentages of the accelerating substance was added and the same steel was subjected to a similar treatment. The following table gives the increase in percentage of the case when certain of' the accelerating substances were added:

Percentage increase Accelerating substance over original depth of case i of 1% nickel oxide 11.3% of 1% chromium oxide 7. i of 1% ferric oxide 13. 2% of 1% manganese oxide (M110 30. 1% of 1% manganic oxide (M11903)- 20. 8%

In another test, a carburlzer was prepared by tumbling the base grains of charcoal and coke with an energizer followed by treatment with a binder such asblack strap molasses and then coating with charcoal dust in order to prevent caking. Test on this carburizing compound showed that the case was .066 inches. A similar compound was made exceptthat finely divided silica dust (SiO amounting to about 2% was added to dry the compound in place of the charcoal and tests under similar conditions showed that the total case had increased to .080 inches, an

increase of 21.2%.

In this test, the steel which analyzed carbon 22%, manganese 353%, silicon 21%, sulphur 022%, phosphorous 019%, chromium 20% of coke and the whole mixed until homogeneit-yresulted. The composition was then dried and used in case-hardenmg an open hearth steel containing 20% of carbon. The

steel was.kept at a carburizing temperature of 900 C. for five hours. The total depth of case was .028 inches, an increase of 12.0 per cent over that obtained by the same carburizer without the addition of the cobalt salt under the same conditions of operation. Furthermore, it is possible with this cobaltcontaining carburizer to obtain satisfactory carburization at a temperature materially below that ordinarily used and at a temperature very near the critical point. Satisfactory carburization, for example, has beenobtained at a temperature'of 780 C. This insures, as hereinbefore pointed out, that the structure of the steel will not be weakened due to excessive grain growth.

The figures given in the above examples are merely indicative of the general elfect of the use of the accelerating substances' in conjunction with carburizing materials and depend on many factors. For this reason, they must not be considered entirely comparable either to each other or to the results obtained with the same percentages using different conditions of operation.

Obviously, also, the product containing the essential ingredients of the carburizer 1ncluding my new and novel idea of using an accelerating substance as here applied may be obtained by other processes and the invention is not to be limited to any particular process of manufacture nor is there any limitation in the proportions of the acceleratmg substances employed in the product s1nce these proportions may be largely varied to suit the particular work for which the carburizer is intended.

I claim:

1. A carburizing composition comprising carbonaceous material, energizing material and an organic salt of a metal (other than the alkali or alkaline earth metals).

2. A carburizing composition comprising carbonaceous material, energizing material and an organic salt of a metal belonging to Group 8 of the Periodic Table.

' 3. A carburizing composition characterized by the presence of carbonaceous material, energizing material and cobalt oxide at the temperature of carburization.

4. A carburizing composition comprising carbonaceous material, energizing material and a cobalt salt of an organic acid.

5. A carburizing compositioncomprising charcoahbarium carbonate and cobalt acetate.

6. A carburizing composition comprising carbonaceous material, energizing material and an accelerating substance, said accelerating substance being characterized by the presence of at least one non-gaseous oxide (other than the alkali or alkaline earth oxides) at the temperature of carburization and being present in amounts between A of 1%and 2%.

7. A carburizing composition comprising carbonaceous material from to 80%, energizing carbonates from 20% to 30%, and an accelerating substance from of 1% to 2%, said accelerating substance being characterized by the presence of at least one nongaseous oxide (other than the alkali or alkaline oxides) at the temperature of carburization. i

8. A carburizing composition comprising 70% to 80% of carbonaceous material, 20% to 30% of energizing carbonates, and A of 1% to 2% of cobalt acetate.

FREDERICK C. LANGENBERG. 

